A common challenge in authentication testing is ensuring ____________.

Non-repudiation refers to the ability to prove that a particular action or transaction has occurred and cannot be denied later. In authentication testing, ensuring non-repudiation is a significant challenge because it requires implementing mechanisms that reliably associate actions with specific users or entities, making it difficult for them to deny their involvement. Strong passwords, secure transmission, and user privacy are all important aspects of authentication testing but do not directly address the challenge of non-repudiation.